Abstract
The dynamics of sperms in the male reproductive organs during copulation was investigated with a nymphalid butterfly, Polygonia c-aureum. It was demonstrated that the males did not transfer all the sperms stored in the duplex to females by one mating. As soon as mating occurred, sperms in the duplex began to flow back to the middle vas deferens, but it seemed to stop on the way of mating. Sperms still remained in the duplex were then ejaculated to the female. This means that part of sperms existed in the duplex before mating were used for the insemination. Since sperms moved from the vas deferens into the duplex again shortly after mating, they probably could be used at the next mating. The significance of this sperm movement specific at mating is discussed.
